The invention relates to the field of electrical exploration. The invention relates to the methods of determination of subterranean formations properties by means of electric parameters of subterranean formations measuring and separating of the parameters measured.
The invention can be applied both in surface and marine electrical exploration using controlled sources of electromagnetic field, and is used in gas and oil exploration for searching and delimitation of oil and gas reservoirs basing on segregation of response from stratum, secondarily changed due to hydrocarbons migration, to split the measured signal to available components. The invention provides for a set of techniques that enable a layer-by-layer determination of geoelectrical parameters values, as well as process characteristics of induced medium polarization and electromagnetic induction.
The known invention ‘A geoelectrical prospecting method (variants)’, Patent RU No. 2235347 published on Aug. 27, 2004, IPC G01V3/06, discloses the way of electromagnetic field inducing in a studied medium by transmitting through it a periodical rectangular pulse sequence with a pause after each pulse. At each current pulse cutoff and between current pulses, during pauses, the momentary values of axial and orthogonal differences of potentials are measured, thus determining potential differences. By solving the inverse problem on a mathematical physics differential wave equation for a dipole source intensity in a polarizable conducting medium, n normalized parameters are calculated following the equation, and the medium model closest to a studied medium in terms of geometrical structure and electric parameters is obtained. According to the electrophysical parameters included in the mentioned equation, time sections of the model are plotted. The method allows detecting and delimitating of oil and gas reservoirs, evaluating of their saturation quality, as well as provides for separation of electrical conduction and induced polarization parameters. Nevertheless the method does not solve the main problem of a quantitative separate studying of the electrical conduction and induced polarization processes, does not consider equivalence of the obtained model electrophysical parameters and can not estimate their informativeness.
The known invention ‘Focused current marine geoelectrical prospecting method’, Patent RU No. 2284555 published on Sep. 27, 2006, IPC G01V3/06, discloses the way of electromagnetic field inducing in a studied medium, measuring of momentary values of the first and the second differences of electric potentials, ensuring of a condition that the resultant of axial electrical potential difference along the section makes zero, calculating of a coefficient basing on the equation, determining of three multitudes of independent normalized electrical parameters, solving of the inverse mathematical problem to determine three electrophysical parameters (conductivity, induced polarization and a constant of the time of induced polarization potential difference drop), and plotting of three time sections basing on those parameters. The essence of the invention is a separation of electrical conductivity and induced polarization parameters. The invention also permits to determine a constant of the time of induced polarization potential difference drop, which is the third important parameter along with the first two ones. Nevertheless the invention provides for only summarized data of all elements of a studied medium, where the field is developed, since a space distribution of monitored source current I is not controlled in any way, and there is no information on the said distribution in existing three-dimensionally inhomogeneous media. The invention does not solve the main problem of a quantitative separate studying of the electrical conduction and induced polarization processes, does not consider equivalence of the obtained model electrophysical parameters and can not estimate their informativeness.
The known invention ‘A geoelectrical prospecting method (variants)’, Patent RU No. 2231089 dated Jul. 8, 2003 published on Jun. 20, 2004, IPC G01V3/06, discloses the way of electromagnetic field inducing in a studied medium by transmitting a periodical rectangular pulse sequence with a pause after each pulse, measuring of electrical potentials differences at points of observation using normalized parameters values and following the mathematical physics differential wave equation for a dipole source intensity in an electrochemically polarizable conducting medium, then solving the inverse problem and determining the inherent electrophysical parameters of each element of medium (conductivity, induced polarization and a constant of the time of induced polarization potential difference drop), and plotting three time sections basing on those parameters. The invention allows detecting and delimitation of oil and gas reservoirs and evaluating of their saturation quality. Separation of electrical conduction and induced polarization parameters is provided. But it does not allow a complete separation of inherent to geological medium elements polarization induced by electrical dynamic transients related to electrical conductivity of the said stratum elements that form the section. The invention does not solve the main problem of a quantitative separate studying of the electrical conduction and induced polarization processes, does not consider equivalence of the obtained model electrophysical parameters and can not estimate their informativeness.
The known invention ‘A method of geoelectrical prospecting signal analysis’, Patent RU No. 2253137 published on Jan. 10, 2005, IPC G01V3/08, discloses simultaneous transforming of each measured signal by at least two modulators, followed by determining of the least intervals. The invention allows increasing of accuracy and informativeness due to a simultaneous analyzing of the signal (regular component) and interference noises (random component). However, the object of the invention is a usage of the method comparing output signals of delta modulators integrators with an output signal of the respective channel with the help of gated comparator. However, the offered method of analysis is feasible only with the use of at least two delta modulators with significantly different quantization steps, system of measuring probes, magnetic field sensors, or any other sensors featuring sufficient broadbandness and spatial angular selectivity (directivity). The method can not be applied for analyzing of parameters obtained by use of the processes of induced polarization in prospecting and exploring of oil and gas fields.
The known invention ‘A method for estimating of specific electrical resistivity of a geological formation enveloping a wellbore filled by a wellbore fluid’, Patent RU No. 2209451 published on Jul. 27, 2003, IPC7 G01V3/38, discloses obtaining of a set of diagrams, choosing of a modeled section, introducing of additionally modeled sections, repeating of correcting of a modeled section until the difference between a diagram and respective modeled diagram becomes below a selected threshold value, and includes correcting of each modeled section as function of the values ratio. The invention provides an improved method evaluating specific electrical resistivity of a geological formation and considering a wellbore fluid invasion into a formation enveloping the wellbore. However, the invention does not allow detecting and delimitation of oil and gas reservoirs, evaluating of their saturation quality, as well as providing of separation of electrical conduction and induced polarization parameters. Besides, the invention does not solve the main problem of quantitative separate studying of the electrical conduction and induced polarization processes, does not consider the equivalence of the obtained model electrophysical parameters and can not estimate their informativeness.
The most close invention in terms of method of geoelectrical characteristics processing is ‘A method for the subterranean formations properties determination’, Patent RU No. 2294547 published on Feb. 27, 2007, IPC7 G01V3/38, that discloses developing of a formation parameters model, modeling of electrical properties measurements, comparing of the modeled measurements and the measured electrical properties, determination of physical/petrophysical properties of formation based on various measurements to provide a combined inversion, evaluating of the physical/petrophysical properties of formation using the model and various measurements of electrical properties, as well as use of a unifying model. The invention allows implementation of improved methods of data processing during a drill well sectioning with the use of electricity, and provides more accurate determination of Rt value to evaluate formation characteristics estimating a formation depth and introducing initial information into the inversion scheme, i.e. geometry information stabilizing imprecise problems of “enhancement”. However, the invention does not allow detecting and delimitation of oil and gas reservoirs, evaluating of their saturation quality, as well as providing of separation of electrical conduction and induced polarization parameters. Besides, the invention does not solve the main problem of quantitative separate studying of the electrical conduction and induced polarization processes, does not consider the equivalence of the obtained model electrophysical parameters and can not estimate their informativeness. The objective of the invention is to imply a method that includes pure adjustment of medium model by iterative use of inversion and separation of the measured signal to any components does not occur. We offer a method that supposes application of medium model obtained as a result of the inverse problem solving, to split the measured signal ΔU(t) into the components EM(t) and Ipg(t).